Not applicable.
Not applicable.
The present invention relates to a combustion chamber assembly, particularly for a vehicle heating device, comprising a combustion chamber housing in which a combustion chamber is bounded by a combustion chamber outer wall, the combustion chamber having a combustion chamber outlet aperture for the exit to a flame tube of exhaust gases produced during combustion.
Such a combustion chamber assembly, such as is generally used in heating devices used as vehicle auxiliary heaters or supplementary heaters, is shown in FIG. 1. This assembly 10s known from the prior art includes a combustion chamber housing 12s which bounds a combustion chamber 16s radially outwardly with an approximately cylindrical outer wall 14a. From a floor region 18s of the combustion chamber housing 12s there extends, coaxially of the outer wall 14s and with respect to a longitudinal axis A of the combustion chamber assembly 10s, an approximately cylindrical inner wall 20s, which is axially closed by a closure region 22s. The outer wall 14s and the inner wall 20s thus define a combustion chamber 16s with an approximately annular shape, which in the region of a corresponding annular outlet aperture 24s is axially open toward a flame tube 26s adjoining the combustion chamber housing 12s. Plural air inlet apertures 28s are provided in the inner wall 20s, and through them, and also by the forwarding effect of a fan (not shown), the combustion air required for combustion can enter the combustion chamber 16s. 
A lining 32s, for example made of nonwoven material or other porous material, is provided on the inner side 30s, facing the combustion chamber, of the outer wall 14a. A lining 36s made of knitted metal fabric can also be provided for sound damping reasons on the inner wall 20s, on its side 34a facing toward the combustion chamber 16s. Fuel is introduced into the combustion chamber 16s by means of a fuel supply duct 39s, for example through an atomizer nozzle (not shown), or else by introduction, for example, into the lining 30s, using an evaporative effect. Furthermore, an ignition element (not shown), for example a glow ignition pin, projects into the combustion chamber 16s, and at the beginning of an operating phase makes sure that the fuel reaching the combustion chamber 16s by atomization or evaporation ignites and that the combustion thus begins.
The exhaust gases produced in the combustion in the combustion chamber 16s or respectively also the combustion flame pass out of the combustion chamber housing 12s in the region of the outlet aperture 24s and flow, as indicated by arrows, through a central aperture 38s of an exhaust gas diaphragm 40s positioned in the flame tube 26s opposite the outlet aperture 24s of the combustion chamber housing 12s. The very hot gases produced by combustion and then flowing along the flame tube 26s pass out of the flame tube in the region of a flame tube outlet aperture 42s and, as likewise shown by arrows, are deflected by a heat exchanger housing, not shown in the Figure, surrounding the flame tube on the outside, so that they flow back on the outside of the flame tube 26s and thereby heat the heat exchanger housing and the medium flowing in the heat exchanger housing. The thus cooled exhaust gases flow back in the direction of the combustion chamber housing 12s and then, after they have if necessary flowed along a partial region of the outside 44s of the outer wall 14s situated remote from the combustion chamber 16s, flow out via an exhaust gas duct system into the environment.
A problem in such combustion chamber assemblies, or heating devices having these, is that a comparatively steep temperature drop is present in the axial direction. The temperature in the region of the flame tube is comparatively high, while the temperature in the region of the combustion chamber housing is comparatively low. Also, the exhaust gases conducted back, if necessary, on the outside of the flame tube are already cooled so far that they can no longer contribute to an appreciable heating of the combustion chamber housing. Coking problems result therefrom in the region of the linings 32s, 36s, the combustion air inlet apertures 28s, and the ignition element (not shown). In particular, when fuel is introduced by means of porous materials, using fuel evaporation, the starting phase, i.e., the phase until the required rated power is reached, becomes very long, above all at very low external temperatures.
The present invention has as its object to develop a combustion chamber assembly of the category concerned, such that the problems arising due to too low temperatures in the region of the combustion chamber housing are substantially eliminated.
According to the invention, this object is attained by a combustion chamber assembly, for a vehicle heating device, comprising a combustion chamber housing in which a combustion chamber is bounded by a combustion chamber outer wall, the combustion chamber having a combustion chamber outlet aperture to exit to a flame tube of exhaust gases produced during combustion, wherein a deflecting arrangement deflects at least a partial stream of the exhaust gases leaving the combustion chamber to flow along at least one partial region of an outer side of the combustion chamber outer wall facing away from the combustion chamber, before entering into the flame tube.
The present invention thus uses at least a portion of the exhaust gases produced in the combustion and thus very hot, in order to conduct these, directly on leaving the combustion chamber housing and still before entering the flame tube, into a region in which they can contribute to substantial heating of the combustion chamber housing. This leads to a marked reduction of the amount of soot accumulating during combustion, and correspondingly also to a marked reduction of the deposits occurring in the combustion chamber region. The heating of the combustion chamber assembly makes sure at the same time that the starting phase can be shortened, since the combustion propagating over the whole combustion chamber will run at a higher temperature from the beginning.
For example, it can be provided that the deflecting arrangement includes a deflecting diaphragm situated opposite the combustion chamber outlet aperture. In order to make sure of a reliable deflection of exhaust gases leaving the combustion chamber, it is proposed that the deflecting diaphragm at least regionally overlaps the combustion chamber housing with a diaphragm outer wall.
The heating of the combustion chamber housing produced according to the present invention does not in general require that the whole of the exhaust gases arising in the combustion are used to obtain heat transfer to the combustion chamber housing. It is therefore proposed that the deflecting diaphragm has in a diaphragm end wall a passage aperture, which is positioned opposite the combustion chamber outlet aperture and preferably has a smaller dimension than the combustion chamber outlet aperture. It is ensured in this manner that only a partial stream of the exhaust gases flowing out of the combustion chamber outlet aperture is deflected for using its heat, while a further portion of the exhaust gases arising in the combustion flows directly into the flame tube.
By the division into two partial streams, namely a main stream which flows directly into the flame tube and a partial stream deflected for heating and only after this conducted into the flame tube, a construction is provided which operates on the injector principle, and in which a reduced pressure is produced by the partial stream flowing directly into the flame tube, and is substantially responsible for the deflection, in a defined manner by means of the deflecting diaphragm, of a portion of the gases or exhaust gases leaving the combustion chamber, to flow around the combustion chamber housing on its outer side.
An embodiment, which is particularly advantageous from the standpoint of flow technology, proposes that the deflecting diaphragm is constituted in a hollow frustroconical shape and that the combustion chamber housing engages into the deflecting diaphragm. It can furthermore be provided that a flow channel region is formed between the deflecting diaphragm and the flame tube, leading the deflected exhaust gas stream toward a flame tube outlet aperture. This flow channel region has a throttling function, so that by means of the rating of the flow cross section in this region, and also taking into account the previously described reduced pressure produced by the main flow going directly into the flame tube, the flow rate of the exhaust gases contributing directly to combustion chamber housing heating can be adjusted,
The present invention furthermore relates to a heating device, particularly for a vehicle, in which heating device a combustion chamber assembly according to the invention is provided.